From c3c4c3f6f9d8e7ce3268a37828fb8343f5d3dad0 Mon Sep 17 00:00:00 2001
From: Andrew Clark <git@andrewclark.io>
Date: Wed, 13 May 2020 11:32:02 -0700
Subject: [PATCH] Fix useMutableSource tearing bug

Fix is to move the entanglement call outside of the block that checks
if the snapshot has changed.
---
 .../react-reconciler/src/ReactFiberHooks.new.js   | 11 ++++-------
 .../react-reconciler/src/ReactFiberHooks.old.js   | 15 +++++++--------
 2 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/packages/react-reconciler/src/ReactFiberHooks.new.js b/packages/react-reconciler/src/ReactFiberHooks.new.js
index 18cbb4f58c428..e2d5244746347 100644
--- a/packages/react-reconciler/src/ReactFiberHooks.new.js
+++ b/packages/react-reconciler/src/ReactFiberHooks.new.js
@@ -997,14 +997,11 @@ function useMutableSource<Source, Snapshot>(
         const suspenseConfig = requestCurrentSuspenseConfig();
         const lane = requestUpdateLane(fiber, suspenseConfig);
         markRootMutableRead(root, lane);
-
-        // If the source mutated between render and now,
-        // there may be state updates already scheduled from the old source.
-        // Entangle the updates so that they render in the same batch.
-        // TODO: I think we need to entangle even if the snapshot matches,
-        // because there could have been an update to a different hook.
-        markRootEntangled(root, root.mutableReadLanes);
       }
+      // If the source mutated between render and now,
+      // there may be state updates already scheduled from the old source.
+      // Entangle the updates so that they render in the same batch.
+      markRootEntangled(root, root.mutableReadLanes);
     }
   }, [getSnapshot, source, subscribe]);
 
diff --git a/packages/react-reconciler/src/ReactFiberHooks.old.js b/packages/react-reconciler/src/ReactFiberHooks.old.js
index d3b83165ea1b2..fc925dbe7bda2 100644
--- a/packages/react-reconciler/src/ReactFiberHooks.old.js
+++ b/packages/react-reconciler/src/ReactFiberHooks.old.js
@@ -986,15 +986,14 @@ function useMutableSource<Source, Snapshot>(
           suspenseConfig,
         );
         setPendingExpirationTime(root, expirationTime);
-
-        // If the source mutated between render and now,
-        // there may be state updates already scheduled from the old getSnapshot.
-        // Those updates should not commit without this value.
-        // There is no mechanism currently to associate these updates though,
-        // so for now we fall back to synchronously flushing all pending updates.
-        // TODO: Improve this later.
-        markRootExpiredAtTime(root, getLastPendingExpirationTime(root));
       }
+      // If the source mutated between render and now,
+      // there may be state updates already scheduled from the old getSnapshot.
+      // Those updates should not commit without this value.
+      // There is no mechanism currently to associate these updates though,
+      // so for now we fall back to synchronously flushing all pending updates.
+      // TODO: Improve this later.
+      markRootExpiredAtTime(root, getLastPendingExpirationTime(root));
     }
   }, [getSnapshot, source, subscribe]);